Driveshaft Gear Rotational Torque

BobMaio

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Jan 6, 2011
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Alpha 1 Gen 2 Sterndrive. I am replacing the driveshaft seal and when reinstalling the nut on the U-Joint assembly, I tightened it to 6.5 rotational inch pounds. The manual calls for 5.25 inch pounds for used bearings and 8 IP for new bearings and warns that if you go over you need to disassemble the gears from the bearing and start over. I guess I am ok with doing that but I need to buy yet another tool to remove the gear from the bearing. So my question: is their any kind of tolerance in that "don't go over" number. Is 6.5 IP going to make that much of a difference? I realize the manual is the gospel in most cases, is that true here as well.
 

Rick Stephens

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So it is NOT tighten to a given torque, but tighten to a ROLLING TORQUE. That requires a torque gauge wrench and not your standard torque wrench.

With Rolling Torque the nut is tightened, however much is required, to where the resistance to turning the shaft and bearings is 6.5 inch pounds. The process requires you disassemble the bearings from the shaft, then reassemble and sneak up on the rolling torque required by tightening a little, check the rolling torque, tighten some more, recheck, etc, until target torque is reached. BTW, I believe ACHRIS has a video on the process.

Realizing you might be doing all that, but kind of responding to racerone's comment.


Short answer: Yes, if you go over, you should split the bearings and start over.

Rick
 

BobMaio

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Rick, thanks. I pretty much figured that. I don't have a bearing splitter big enough to do the job so I may have to go to a marina and see if I can talk them into splitting it. Now correct me if I am wrong, but all I need to do is separate the bearing from the gear just a small amount. I am thinking 1/8 inch, then when I reapply the nut and toque it correctly it will bring the bearings back in contact with the gear face. I don't have to pull everything apart completely correct?. Also, I assume this does not harm the bearings.

FYI, when I assembled the assembly this afternoon, I thought I was creeping up on the 5 IP setting. So if anyone is reading this, go real slow with minor tightening of the nut. What a pain in the butt.
 

Rick Stephens

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When I did mine last time I just separated a little bit and snuck up. Not to degrade that method, as I have only done rolling torques several times. In my case after only separating a teensy bit, first time out within about 5 minutes I had a rumble. Took it back apart and found it was really loose. In that case I re-torqued and haven't had issue since. But the results were definitely hard to get perfect when I started from split only a little. That said, I'd probably do it again :D
 

BobMaio

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Rick, so it would be better to create a bigger separation between the bearing and the gear face.
 

muc

"Retired" Association of Marine Technicians...
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At MerCruiser school, they teach us to loosen the nut 1/2 turn and hold the bearing race closest to the gear the the gear facing up. Now lightly tap the threaded end of the shaft a few times. This will be enough to loosen the rolling torque enough to start over.
 

harringtondav

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Alpha 1 Gen 2 Sterndrive. I am replacing the driveshaft seal and when reinstalling the nut on the U-Joint assembly, I tightened it to 6.5 rotational inch pounds. The manual calls for 5.25 inch pounds for used bearings and 8 IP for new bearings and warns that if you go over you need to disassemble the gears from the bearing and start over. I guess I am ok with doing that but I need to buy yet another tool to remove the gear from the bearing. So my question: is their any kind of tolerance in that "don't go over" number. Is 6.5 IP going to make that much of a difference? I realize the manual is the gospel in most cases, is that true here as well.
When you replace the gear yoke seal the yoke shaft slides out of the assembled gear and bearings and spacer. These remain pressed together at whatever preload existed before disassembly.

The tricky part is getting the rolling torque correct on reassembly. The nylock nut holding it all together uses up much of the rolling torque spec. This can fool you into thinking you're close to socked up when things are still loose.

The nut's threads are 5/8-18. .055" per turn. I put a.007" feeler under the nut and carefully tighten it until the feeler starts to catch. That gives you 1/8 wrench turn until the nut contacts the washer. Eyeball your wrench this 1/8 turn and switch to you in/lb wrench. Check torque, switch back to the ratchet and give it another 1/8 turn. Recheck with the in/lb. Repeat carefully until the torque increases a bit from your starting point, and then until it comes w/in spec.

And the spec is correct. These bearings run under very high compressive and bending/radial loads. The new bearing higher torque allows for new bearing "wear in" and minor loosening. Low preload will be a disaster. Not for the bearings, but for the upper gear set as the driven gear deflects out of mesh.
 

BobMaio

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Without sounding really stupid, I need some verification. I finally received the bearing separator tool so now I want to get on with the job. My understanding is that I am separating the two bearings from each other.. Not the bearing closet to the gear from the gear. Once there is a space between the 2 bearings I can proceed with the rolling torque. When the manual says to "start over" do they really mean pull all the bearings off the shaft? From what I understand of the process, you push the bearing (smaller of the two onto the shaft so it is tight against the gear. Then press the second bearing on leaving a small gap. If I pull all the bearings off the shaft, what would I be gaining? So thanks again in advance if you could verify my understanding. Or if I am off, please try to explain where. Thankyou.
 

todhunter

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I think by start over they mean separate the two bearings again. A small distance should do it. I don't think you'll need to remove the bearing from the shaft.
 

harringtondav

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Without sounding really stupid, I need some verification. I finally received the bearing separator tool so now I want to get on with the job. My understanding is that I am separating the two bearings from each other.. Not the bearing closet to the gear from the gear. Once there is a space between the 2 bearings I can proceed with the rolling torque. When the manual says to "start over" do they really mean pull all the bearings off the shaft? From what I understand of the process, you push the bearing (smaller of the two onto the shaft so it is tight against the gear. Then press the second bearing on leaving a small gap. If I pull all the bearings off the shaft, what would I be gaining? So thanks again in advance if you could verify my understanding. Or if I am off, please try to explain where. Thankyou.
I agree with todhunter and Rick. Wedging a separator between the spacer and either bearing, just a touch, will relieve the press fit load on the two bearings. Then try again. Just be careful to not raise a burr on the aluminum spacer. It could compress under thrust load and leave you loose.

I've over torqued once or twice. I grumbled and went back to my press. Pressing the bearings and spacer onto the gear takes some finesse. Lube the gear hub well, and press slowly so the stick-slip doesn't grab the assembly too tight. I put a piece of card stock ...about .006" between a race and the spacer. When it starts to drag, I stop and go to the inch pound process I mentioned above.
 

BobMaio

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I agree with todhunter and Rick. Wedging a separator between the spacer and either bearing, just a touch, will relieve the press fit load on the two bearings. Then try again. Just be careful to not raise a burr on the aluminum spacer. It could compress under thrust load and leave you loose.

I've over torqued once or twice. I grumbled and went back to my press. Pressing the bearings and spacer onto the gear takes some finesse. Lube the gear hub well, and press slowly so the stick-slip doesn't grab the assembly too tight. I put a piece of card stock ...about .006" between a race and the spacer. When it starts to drag, I stop and go to the inch pound process I mentioned above.
Thanks everyone for your help. I was able to separate the bearings and redid the rotational torque to a value between 4.5 and 5 IP. The manual calls for 5 IP but when I got that close I decided any additional tightening would bring me over the 5 limit. Now having done this, I realize that what I should have done when I replaced the seal was to separate the bearings slightly and start with a fresh low torque setting as I finally did. Instead I started with the bearings tight against each other preventing me from creeping up on the correct torque.
 

Rick Stephens

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At MerCruiser school, they teach us to loosen the nut 1/2 turn and hold the bearing race closest to the gear the the gear facing up. Now lightly tap the threaded end of the shaft a few times. This will be enough to loosen the rolling torque enough to start over.
I keep bringing my thoughts back to how elegant this solution is. I don't have a problem with how BobMaio and I did it, with a splitter. Next time I am going to do muc's method.

Rick
 

DanD34

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Aug 3, 2019
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I know this thread is a couple months old but I just wanted to comment. I put a new input shaft and seal in my outdrive last winter. I read about this procedure and while easy to understand seems it would be tedious to perform and easy to make mistakes. I'm glad my gen 1 is old enough that it had the spacer between the bearings that sets the preload. Just tighten the nut to the specified torque value ( I can't recall the value at the moment but it's pretty high) and you're done. Seemed to work well all last summer and still no oil leak into the bellows!
 

Rick Stephens

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I know this thread is a couple months old but I just wanted to comment. I put a new input shaft and seal in my outdrive last winter. I read about this procedure and while easy to understand seems it would be tedious to perform and easy to make mistakes. I'm glad my gen 1 is old enough that it had the spacer between the bearings that sets the preload. Just tighten the nut to the specified torque value ( I can't recall the value at the moment but it's pretty high) and you're done. Seemed to work well all last summer and still no oil leak into the bellows!
Merc engineers changed it to the rolling torque method from the plain old spacer and torque to value. My bet is that more heat is generated at the higher torque setting used on the older spacer torque units and in the long run this caused more bearing failures than were acceptable.

Rolling torque is fairly common in heavy equipment gearboxes. As you noted, takes more training and tooling to use t. Like you, I preferred doing it the old way ;^)

Rick
 

DanD34

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Rolling torque is fairly common in heavy equipment gearboxes. As you noted, takes more training and tooling to use t. Like you, I preferred doing it the old way ;^)
Yes....if you look at reassembly procedures for something like old tractor transmissions and differentials ( I'm not familiar with modern ones...I'm familiar with stuff made from the 40s to the 70s) you see tolling torque specs all over.
 
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